Amiga Technical Resource - Fitting a PLCC socket

Fitting a PLCC socket to hold a device previously soldered to the PCB

A common device to fail in "classic" Amigas is the 8520 CIAs (complex interface adaptors). There are two of these on almost every Amiga model; their job is to communicate single line I/O information directly to and from the computer's data bus.
Some of their jobs include much of the parallel and serial port I/O, handling keyboard serial data, turning the audio filter on and off, floppy disk control I/O, and more. Because the CIAs are almost directly connected to the outside world, they can sometimes be damaged through the parallel, serial or floppy ports.
On older Amigas, they were a DIL (dual in line) package device fitted into sockets, meaning you could easily replace them. All surface mount technology machines (A600, A1200, A4000) have these devices in the PLCC (plastic leaded chip carrier) package instead and are permanently soldered to the motherboard, making them a bit trickier to replace.

Fortunately there is a simple solution to this problem. It involves unsoldering the device and fitting a surface mounted PLCC socket.
You can do this in the process of replacing a damaged one, or you can simply remove a working device and fit it into a socket.

This image shows an A4000D with the CIAs U300 and U350 fitted into PLCC sockets:

This technique can be applied to any of the PLCC devices on the Amiga motherboard, at least with A4000 models. The more compact A600 and A1200 had less area available, so socket space was sacrificed. Some sockets could still be fitted, but this may involve moving components and modifying the socket.

In this example, I'll be removing U400 (Paula) in an A4000D and fitting a 52 pin PLCC socket to hold it. Paula is the device responsible for RS232 port and floppy drive serial data, digital to analogue audio conversion (sound generation) and reading the analogue input pins on the mouse/game ports.

Once you have all the tools required, the very first thing to do is get the correct PLCC socket. There are two types, surface mount (SMD/SMT) and through hole. Of course you need the surface mount variety. Count the number of pins the PLCC device has. The CIAs have 44 pins, Paula has 52 pins. You need the PLCC socket with the same number of pins.

Don't forget you can click on these images for a larger version.

Never attempt using a used or cracked socket, use a new one every time, otherwise you'll be forever plagued with intermittent problems caused by the socket not reliably contacting the PLCC device.
Check on the bottom side for any location assist pegs or dimples. Commodore have two corner holes in the PCB for socket locating pegs, but it's unlikely you'll be able to get sockets with matching pegs.
If your socket has pegs/dimples and they don't fit Commodore's peg holes, then use small side-cutters to chop them off. Use a craft knife to trim away the cut plastic to a smooth surface.
Here's the bottom side of the socket I used, there were no pegs on this one, it was flat underneath. No modification was necessary.
Next apply a little SMD flux to the legs of the PLCC you're going to remove. This makes the solder a bit easier to work with.
Fit a small or medium (2-6mm inside diameter) single tube nozzle to the hot air rework tool. Set the heat to medium-low and the air speed to low.
You can see below I've used a heat setting of 3 and an air speed of 2. Switch the tool on and leave it to heat up for about a minute.
Hold the hot air tool in your left hand (if you are right handed). Position tip of the tool's nozzle about 10cm above the board and gently pre-heat the area for a few seconds, this reduces stress on the circuit board and surrounding components.
Now hold the tip of the nozzle about 2cm above the PLCC we're removing. Move the nozzle about in a circular pattern above the body of the PLCC so the hot air evenly heats all of the solder joints.
Important! Never hold the nozzle in one spot when it's close to the PCB! Keep it moving all the time, otherwise the concentrated heat in one area can scorch the circuit board or cause it to blister.
The solder should suddenly melt in around 10-20 seconds. With a pair of fine tipped tweezers in your right hand (if you are right handed), gently keep touching the side of the PLCC body or trying to lift one side. When the solder melts, it'll move slightly.
Grab onto one of the legs with the tweezers and lift the PLCC directly upwards. Avoid sliding it sideways too much, as the solder joints of surrounding components will probably be melted as well. Touching other components will disturb their position. Remove the tool's nozzle away from the board immediately.
Turn off the hot air tool, or put it aside where the hot air isn't going to blow on anything like your workbench. Be careful as the metal nozzle is extremely hot!!!
Using solder wick, clean all the old solder from the board's solder pads.
Using isopropyl alcohol, SMD flux cleaner or methylated spirits, clean the circuit board. Scrub it with an old toothbrush or small paint brush and wipe it clean using a rag or cloth.
It's important that all surfaces to be soldered are smooth and clean for a reliable joint to be made.
Turn the PLCC device upside-down and carefully use solder wick to remove most of the old solder from the legs. This is important, as lumps of solder left on the legs can damage the contacts in the PLCC socket when you insert and remove the device.
Avoid overheating or bending the legs while doing this.
Using a fibreglass brush, remove any last traces of solder to leave the legs looking shiny and new.
Just brush it enough to leave a smooth surface. Avoid brushing too much as it will remove the tin coating, exposing the bare copper of the leg.
Next we're ready to fit the new PLCC socket. Apply a little SMD flux to the legs underneath the socket.

And to the pads on the board. This makes the solder flow and attach itself to the metal much easier.
Get the solder paste syringe and squirt a bit out onto a piece of scrap paper to make sure you've got a nice clean flow. Draw a thin line down each row of solder pads as shown below.
You don't need as much solder paste as you might think, the amount shown here is about right. Too much paste and it'll bridge legs together when you heat it. Too little and you won't have a reliable solder joint. If anything, it's better to have too little rather than too much. It's a lot easier to add a little more paste and heat it if you have to, as opposed to removing excess solder.
Try and get the line of solder closer to the inside edge of the pads, as this is where you'll be heating it next.

Tip: store your solder paste in the refrigerator when you're not using it.
This slows it from drying out and it's still perfectly usable many months, even years past its expiry date.
Locate the pin 1 marker on the socket. It's usually an arrow/triangle like in the picture below, (bottom centre) or a dot on the top edge of the socket. This must line up with the pin 1 indicator on the motherboard, this is the V marker in the side of white silkscreen square.

Place the socket onto the solder pads. You need to carefully line each side up so the pins in the socket line up right in the centre of the pads on the motherboard.
This can be tricky to see with the solder paste in the way, but you will be able to see the PCB tracks, as many run off from the centre of the solder pads.
There are two ways to solder on the socket. Using hot air, or by hand soldering.
With hot air, you need to have a very small nozzle; otherwise the plastic socket will get melted due to the large spread of hot air.
For this example, I'll use a hand soldering technique. I'll change my soldering iron tip from the general purpose "K" tip, to an ultra fine needle tip.
Due to the lesser heat transfer ability of the needle tip, you may have to use a higher than normal soldering temperature, probably around 400°C.
Make sure the soldering iron tip is properly cleaned and well tinned. You can get special tip cleaning pots of solder particles and cleaning paste as shown below.
Check once more you have the pin 1 marker where pin 1 should be and solder a single corner pin only.

Check the alignment in the centre of the solder pads is still good. If the socket has slipped, heat the pin again to melt the solder and gently slide the socket slightly to correct the alignment.
Now solder each of the pins in turn to melt the solder paste. Each pin will need 3-4 seconds of heat to ensure all of the solder paste has melted underneath the socket pin.
Once complete, visually inspect your work for any solder shorts or bridges. Look carefully under the socket as far as you can. If the bridge is small, you can often use the soldering iron to "wipe" along between two pins, drawing the iron from the outside of the bridge towards the centre of the socket.
If there is too much solder and the bridge will not clear easily, you'll need to use some solder wick to remove the excess solder. You may have to change back to a larger tip for this.

Check for unsoldered pins by drawing a sharp point, such as a scriber, along the top of the rows of soldered pins.

If any pins bend sideways when touched, it indicates an unsoldered joint. Apply a tiny spot of solder paste on top of the pin and heat it with the soldering iron to melt the solder.
The job is nearly complete. Visually check once more for solder shorts. If in doubt, use a multimeter in the ohms range to check adjacent pins for shorts.
Once you're confident all the joints are correctly soldered, insert the PLCC device. Taking care to line up pin 1, press it down firmly and it will click into place.
Power the computer on and check the operation. If it does not work correctly, power it off immediately. Check again for unsoldered pins in the socket. Use a multimeter to test adjacent pins for shorts (I.E. measure each side-by-side pair for short circuits).
Lastly, to remove a socketed device, the correct way is to use a PLCC extraction tool, these are cheaply and easily available from most electronics and computer shops.

If you try using something else such as tweezers or screwdrivers, you'll most likely crack the socket, which will require replacement.
To use the extractor, just put the hooks into the matching slots and squeeze the sides.

Questions, comments, errors? Email me.